Strasburg immediately looked down at his right arm and then shook it around after throwing his 56th pitch of the night. ... Despite pleas from Strasburg to remain in the game, Riggleman wouldn't listen to his rookie pitcher. Strasburg departed with a disgusted look on his face.

In 4 1/3 innings, Strasburg gave up two hits, one run and struck out six.

He was making his third start since returning from a stint on the DL with inflammation in the back of his right shoulder. He will have an MRI on his right arm Sunday.

“You’re always concerned when a pitcher leaves. We’ll see what the MRI says,” Rizzo said.

Craig Stammen relieved Strasburg with the Nationals leading the Phillies 5-1. The Nats went on to win, 8-1.

The Nationals will surely be cautious with Strasburg. The No. 1 overall pick in the 2009 draft, he was scratched minutes before his scheduled start against Atlanta on July 28 and was diagnosed with inflammation in his right shoulder. He was placed on the 15-day disabled list the next day.

When healthy, Strasburg has been as good as advertised. He’s 5-3 with a 2.91 ERA and has allowed two or fewer earned runs in nine of 12 starts. He was throwing in the high 90s mph all night and had shut down the two-time defending NL champs.

Strasburg’s first pitch of the game was a 97 mph fastball to Jimmy Rollins. Four pitches later, Strasburg struck out the former NL MVP looking on a buckling 83 mph curve.